<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .item1{
            font-size: 16px;
        }
        .item2{
            font-size: 1rem;
        }
    </style>
</head>

<body>
<div class="item1">
    这是16px大小
</div>
<div class="item2">这是rem文字大小</div>
</body>

</html>